Deposits of various materials and alloys are extensively used in a wide variety of functional and decorative applications. Typical metals are zinc, copper, cadmium, chromium, nickel, cobalt, gold, silver, palladium, platinum, ruthenium, and alloys of these metals with each other and with tin and lead. These materials and alloys are often used on decorative and functional articles to prevent tarnishing surface corrosion, or to provide a smooth, lustrous surface.
These electrolytic deposits are also used in a large variety of electronic surfaces, electronic devices, and electronic conductors. They are used as protective layers to prevent corrosion of other underlying materials and to maintain good surface electrical contact. Such deposits are also used in the fabrication of integrated circuits and to provide conducting paths and places to mount electronic components. Such uses are increasing rapidly and represent an important commercial use of electrolytic deposition processes.
Commercially, it is highly desirable to be able to plate very rapidly and maintain good quality deposits for the particular application at hand. Smooth deposits are particularly important because it yields good surface electrical contacts and insures low porosity for the plating thickness attained. In addition, it is desirable to have relatively constant plating thickness so as to ensure complete coverage without excessive build-up of plating thickness.
In the fabrication of integrated circuits where close dimensional tolerances are required, it is highly desirable to have smooth platings with constant thickness. A particular freedom from dendritic growth precludes any chance of shorts across conductive paths from needle growth. In addition, constant plating thickness is highly advantageous to obtain the close tolerances required.
Various references have disclosed the use of additives to electroplating solutions. Some of these references are: W. E. Rosenberg, et al., U.S. Pat. Nos. 3,956,123, issued May 11, 1976; S. P. Valayil, 3,749,646, issued July 31, 1973; K. Nishihava, 3,661,730, issued May 9, 1972; B. D. Ostrow, et al., 4,000,047, issued Dec. 28, 1976; and W. F. Rosenberg, et al., 3,875,029, issued Apr. 1, 1975.